UK banking group Lloyds is to sell a portfolio of US residential mortgage backed securities (RMBS) for 3.3bn pounds as it continues to dispose of non-core assets to boost capital.The portfolio has a book value of £2.7bn so the bank will pocket a gain of £540m before tax on the sale which will be used for "general corporate purposes"."The transaction is part of the group's continued capital accretive non-core asset reduction," Lloyds said on Friday morning.The Lloyds TSB Group Pension Trust also sold its share of the RMBS portfolio with a book value of £805m, realising a pre-tax gain on the sale of £360m which will reduce the deficit.The gain on sale, the reduction in risk-weighted assets and the trimmed pension deficit will result in Lloyds' core tier-one capital ratio under current capital rules increasing by 33 basis points (£950m capital equivalent).